I have been having the problem for a while too. Almost a year at this point. Today, I finally decided to toy with the settings a little bit. I went into the EPST Edit Mode (##778#) and tried all the things that everyone has suggested so far. That didn't work, so I tried the following. So far I have not seen the 4G break connection and I have run multiple successful speed tests with no break in connection. Modem Settings->Preferred Mode (Automatic), Preferred Mode(9k) (LTE only), Rev. A (eHRPD). I hope this helps.